Greater New Orleans

A short segment of Interstate 10 between the hurricane levee in easternmost New Orleans and the north up ramp onto the twin spans bridge to Slidell is only 7 feet above sea level, leaving its use as a main evacuation route vulnerable to hurricane storm surges. That vulnerability could increase in the future if the Chandeleur Islands continue to rapidly erode, said Ezra Boyd, a risk consultant working with the Lake Pontchartrain Basin Foundation.
(Ezra Boyd, Lake Pontchartrain Basin Foundation)

In a presentation to the Southeast Louisiana Flood Protection Authority-East on Thursday, Boyd said a new analysis indicates that a segment of Interstate 10 in eastern New Orleans between the new levee just completed by the Army Corps of Engineers and the twin span bridges leading to Slidell is only 7 feet above sea level and will be inundated by storm surges and waves well in advance of a hurricane.

State and local evacuation planners estimate the time that low points on evacuation routes outside local levee systems will be inundated by surge and waves to set the cut-off time for their use.

But Boyd said that based on new computer storm surge modeling, if the Chandeleur Islands continue to erode, storm surges at the New Orleans side of the bridge will soon be a half-foot higher and reach the 7-foot level an hour earlier.

A 2008 study of evacuation traffic found that a maximum 2,000 vehicles an hour use I-10 to travel north, meaning that the earlier arrival of surge could result in as many as 5,000 fewer people being able to evacuate, Boyd said.

Boyd said his study found another evacuation concern involves traffic using bridges that go over the Industrial Canal. The problem there is that evacuation traffic might be competing with ship and boat traffic trying to exit the Industrial Canal and the Gulf Intracoastal Waterway in advance of a hurricane.

The ship traffic faces new Coast Guard restrictions in the aftermath of Hurricanes Katrina and Gustav that require most to leave, and leave earlier, from the Industrial Canal. There are five drawbridges over the Industrial Canal that are used during evacuations, some of which take a significant amount of time to open and close to accommodate ship traffic.

Boyd said the study is aimed at assuring that evacuation planning is added into the decision making used by federal, state and local planners as they consider how to operate the new levee system and how they explain to the public when and how they evacuate in advance of hurricanes.

Levee authority members pointed out that a similar concern already was raised with the Army Corps of Engineers about a segment of Interstate 10 that runs west through St. John the Baptist, St. James and part of Ascension parishes. Parish officials urged the corps to build the proposed West Shore Lake Pontchartrain levee system on the wetland side of the highway through all three parishes, but the corps decided the levee would only be built through St. John, and that money would be included in the project to raise homes and businesses in flood prone areas of St. James and Ascension parishes.

While the corps plan does include some improved protection for the evacuation route portion of I-10, the plan is not as comprehensive as parish and levee authority officials would like.

The study is one of several that have been either sponsored by the levee authority or by non-profit groups and then presented to the authority that are aimed at assisting in outlining risk-related issues the state and the levee authority should consider in advance of future requirements that the levees be certified as meeting the protection standards required by the National Flood Insurance Program, which is protection from surges caused by a hurricane with a 1 percent chance of occurring in any year, the so-called 100-year storm.

The levee authority has also been couching its planning efforts in the context of increasing the level of protection to include surges caused by hurricanes with a 0.2 percent chance of occurring in any year, a 500-year storm.